The present invention generally relates to optical memory and more particularly, to a method of manufacturing an optical memory element for optically recording and reproducing information.
In recent years, particular attention has been directed to an optical memory device as a memory unit with a large capacity and also a high density. The reason why the optical memory device can provide the high density and large capacity that, since the bit, which is a recording unit of information, is determined only by a beam diameter of light, its configuration may be formed to have a size approximately in the order of one .mu.m in diameter. The above fact, however, imposes various limitations on an optical memory device. More specifically, in order to record information at a certain predetermined position or to reproduce information recorded at a certain predetermined position, it becomes necessary to position a light beam extreme accuracy.
Generally, in an optical memory device used exclusively for reproduction, address information can be preliminarily included in the recorded bit, thus making it possible to position the light beam during reproduction of the recorded information, but in an additionally recorded memory or in a memory capable of being rewritten, it is extremely difficult to record the address information simultaneously during the information recording. Accordingly, with respect to the additionally recorded memory or in the memory which can be rewritten, there has been adopted a practice to have certain guide tracks or guide addresses preliminarily included in a memory substrate.
By way of example, as illustrated in FIG. 9 showing a fragmentary perspective view of a conventional memory substrate for an additionally recorded memory or a memory capable of being rewritten, it has been a common practice to form concave and convex grooves g in a substrate S for recording or reproducing information along said grooves g. These concave and convex grooves g have a configuration intermittently extending in a circumferential direction of the substrate S, thereby to impart bit information indicating addresses of the grooves g.
There have already been proposed several processes for forming such concave and convex grooves, which may be broadly divided into the following three kinds of practices.
(i) A process which employs acrylic resin or polycarbonate resin so as to form the concave and convex grooves as described above by injection molding. By this molding, configurations of an Ni stamper preliminarily formed with the guide tracks and guide addresses are copied or transcribed.
(ii) A casting process in which molten acrylic resin is poured into the Ni stamper preliminarily formed with the guide tracks and guide addresses as described above for curing or hardening through heating.
(iii) A so-called "2P" process in which an ultraviolet curing resin is poured between a substrate such as an acrylic resin substrate, glass substrate or the like and the Ni stamper preliminarily formed with the guide tracks and guide addresses as described above for irradiation thereonto of ultraviolet rays through said substrate, so as to cure or harden said resin, with a subsequent removal of said Ni stamper.
However, since each of the above processes employs a resin, there is a possibility that oxygen or moisture, etc. undesirably reaches a recording medium through the resin, thus resulting in such a disadvantage that the recording medium is deteriorated in quality.
In order to overcome the inconvenience as described above, the present inventors have already proposed in Japanese Patent Application Tokugansho No. 58-84613, a manufacturing process including steps of applying a photo-resist material onto a glass substrate, further applying a laser beam to the photo-resist material for recording guide patterns (guide tracks and guide addresses), and subsequently, forming grooves in the form of the guide patterns by etching.
The above process, however, still has a disadvantage in that, since each of the guide patterns must be successively recorded for each track by the laser beam, a long time is required for the recording and thus, the process is not fully suited to mass-production.